Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS4204150 A
Publication typeGrant
Application numberUS 05/951,955
Publication dateMay 20, 1980
Filing dateOct 16, 1978
Priority dateJun 20, 1978
Also published asCA1106916A, CA1106916A1
Publication number05951955, 951955, US 4204150 A, US 4204150A, US-A-4204150, US4204150 A, US4204150A
InventorsSerge Mathieu
Original AssigneeH.O.P. Consulab Inc.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Apparatus and method for regulating the power factor in an electrical distributing-network line
US 4204150 A
Abstract
The specification discloses an apparatus and a method for regulating the power factor in an electrical distributing-network line; according to one embodiment of the invention, the active line power is measured by means of a transducer, the output from which is a continuous voltage proportional to the active power supplied by the line; the reactive power of the line is then measured by means of a second transducer, the output from which is also a continuous voltage proportional to the reactive power supplied by the line; the voltage supplied by the active-power transducer is then divided by voltage dividers in order to obtain two reference voltages L1, L2, the values of which indicate the fixed limits for the line power factor; the voltage supplied by the reactive-power transducer is then compared with reference voltages L1, L2 for the purpose of obtaining two logic levels indicating one of the three following operations: one or more capacitors are connected if the power factor is below the limit L1 and is inductive; one or more capacitors are disconnected if the power factor is above the limit L2 and is inductive; no action is taken if the power factor is above the limit L1 and below the limit L2 and is inductive.
Images(3)
Previous page
Next page
Claims(18)
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A method for regulating the power factor in an electrical distributing-network line, comprising:
(a) measuring a first component of the line power by means of a transducer, the output from which is a continuous voltage proportional to said component of the power supplied by the line;
(b) measuring a second component of the line power by means of a transducer, the output from which is a continuous voltage proportional to said second component of the power supplied by the line;
(c) dividing the voltage supplied by the first component by means of voltage dividers to obtain two voltages L1 and L2, the values of which represent the limits prescribed for the power factor in the line;
(d) comparing the voltage supplied by the transducer of the second component with reference voltages L1 and L2 to obtain two logic levels indicating one of the following three operations:
(i) connecting one or more capacitors if the power factor is below said limit L1 ;
(ii) disconnecting one or more capacitors if the power factor is above said limit L2 ;
(iii) carrying out no operation if the power factor is above said limit L1 and below said limit L2.
2. A method for regulating the power factor in an electrical distributing-network line, consisting in:
(a) measuring the active power in the line by means of a transducer, the output from which is a continuous voltage proportional to the active power supplied by the line;
(b) measuring the reactive power in the line by means of a transducer, the output from which is a continuous voltage proportional to the reactive power supplied by the line;
(c) dividing the voltage supplied by the active-power transducer by means of voltage dividers, in order to obtain two reference voltages L1 and L2, the values of which represent the limits prescribed for the line power factor;
(d) comparing the voltage supplied by the reactive-power transducer with reference voltages L1 and L2, to obtain two logic levels indicating one of the following three operations:
(i) connecting one or more capacitors if the power factor is below said limit L1 ;
(ii) disconnecting one or more capacitors if the power factor is above said limit L2 ;
(iii) carrying out no operation if the power factor is above said limit L1 and below said limit L2.
3. A method for regulating the power factor in an electrical distributing-network line, consisting in:
(a) measuring the active power in the line by means of a transducer, the output from which is a continuous voltage proportional to the active power supplied by the line;
(b) retaining the voltage obtained;
(c) measuring the reactive power in the line by means of said transducer and of a potential phase shifter, to obtain, at the output from the transducer, a second voltage proportional to the reactive power supplied by the line;
(d) retaining the second voltage obtained;
(e) dividing the voltage proportional to the active power, in order to obtain two reference voltages L1 and L2, the values of which represent the limits prescribed for the line power factor;
(f) comparing the second voltage obtained with reference voltages L1 and L2, in order to obtain two logic levels indicating one of the following three operations:
(i) connecting one or more capacitors if the power factor is below said limit L1 ;
(ii) disconnecting one or more capacitors if the power factor is above said limit L2 ;
(iii) carrying out no operation if the power factor is above said limit L1 and below said limit L2.
4. A method according to claim 1, 2 or 3, consisting in disconnecting one or more capacitors if the power factor becomes capacitive independently of the value of the power factor in relation to said limits L1 and L2.
5. A method according to claim 1, 2 or 3, comprising a real-time clock determining the period of each capacitor connecting or disconnecting operation.
6. A method according to claim 1, 2 or 3, comprising an alarm indicating that the number of capacitors energized is insufficient.
7. A method according to claim 1, wherein the first component is measured by means of a volt-amperes transducer and the second component is measured by means of a watts transducer.
8. A method according to claim 1, wherein the first component is measured by means of a volt-amperes transducer and the second component is measured by means of a vars transducer.
9. An apparatus for regulating the power factor in an electrical distributing-network line, said apparatus comprising:
(a) transducer means for measuring a first component of the line power, said means comprising an output representing a continuous voltage proportional to said component of the power supplied by the line;
(b) transducer means for measuring a second component of the line power, said means comprising an output representing a continuous voltage proportional to said second component of the power supplied by the line;
(c) means for dividing the voltage supplied by the transducer of the first component, to obtain two reference voltages L1 and L2, the values of which represent the limits prescribed for the line power factor;
(d) means for comparing the voltage supplied by the transducer of the second component with reference voltages L1 and L2, in order to obtain two logic levels indicating one of the following three operations:
(i) connecting one or more capacitors if the power factor is below said limit L1 ;
(ii) disconnecting one or more capacitors if the power factor is above said limit L2 ;
(iii) carrying out no operation if the power factor is above said limit L1 and below said limit L2.
10. An apparatus for regulating the power factor in an electrical distributing-network line, said apparatus comprising:
(a) transducer means for measuring the active power in the line, said means having an output representing a continuous voltage proportional to the active power supplied by the line;
(b) transducer means for measuring the reactive power in the line, said means having an output representing a continuous voltage proportional to the reactive power supplied by the line;
(c) means for dividing the voltage supplied by the active-power transducer, in order to obtain two reference voltages L1 and L2, the values of which represent the limits prescribed for the line power factor;
(d) means for comparing the voltage supplied by the reactive-power transducer with reference voltages L1 and L2, to obtain two logic levels indicating one the following three operations:
(i) connecting one or more capacitors if the power factor is below said limit L1 ;
(ii) disconnecting one or more capacitors if the power factor is above said limit L2 ;
(iii) carrying out no operation if the power factor is above said limit L1 and below said limit L2.
11. An apparatus according to claim 10, wherein the divider means comprise two graduated potentiometers to divide the voltage supplied by the active-power transducer, in order to define said reference points L1 and L2.
12. An apparatus according to claim 8 or 9, said apparatus comprising means for determining whether the power factor is capacitive.
13. An apparatus according to claim 10, comprising electronic flip-flops, the purpose of which is to connect and disconnect capacitors in sequence.
14. An apparatus according to claim 13, said apparatus comprising a real-time clock used to determine the period of each electronic flip-flop operation.
15. An apparatus according to claim 10, said apparatus comprising an alarm indicating that the number of capacitors connected is insufficient.
16. An apparatus for regulating the power factor in an electrical distributing-network line, said apparatus comprising: transducer means to measure the active power in the line, said means comprising an output representing a continuous voltage proportional to the active power supplied by the line; means to retain the voltage thus obtained; means for connecting a potential phase-shifter system at the input to said transducer means, for obtaining, at the output from said transducer means, a voltage proportional to the reactive power supplied by the line; means for retaining said voltage proportional to the reactive power; means for dividing the retained voltage proportional to the active power in the line, to obtain two reference voltages L1 and L2 ; means for comparing the retained voltage proportional to the reactive power in the line with reference voltages L1 and L2, the result of this comparison providing two logic levels indicating one of the following three operations:
(i) connecting one or more capacitors if the power factor is below said limit L1 ;
(ii) disconnecting one or more capacitors if the power factor is above said limit L2 ;
(iii) carrying out no operation if the power factor is above said limit L1 and below said limit L2.
17. An apparatus according to claim 9, said apparatus comprising a volt-amperes transducer for measuring the first component and a watts transducer for measuring the second component of the power supplied by the line, said dividing means defining the fraction of the volt-amperes to be represented by the watts in order that the power factor may remain within the limits L1 and L2.
18. An apparatus according to claim 9, said apparatus comprising a volt-amperes transducer for measuring the first component of the power supplied by the line and a vars transducer for measuring the second component of the power supplied by the line, said dividing means defining the fraction of volt-amperes to be represented by the vars at the L1 and L2 limits established.
Description

The object of the present invention is an apparatus and a method for regulating the power factor in an electrical distributing-network line.

It is known that in an industrial electrical installation having a large number of inductive loads, the power factor may easily be below 70%. Since many companies providing electrical service impose a surcharge whenever the power factor is below 90%, it would appear to be useful and profitable to establish a corrective system to keep the power factor within reasonable limits, in order to avoid paying this surcharge.

There are two known ways of regulating the power factor. The first is by introducing capacities into the transmission lines; the second is by simulating these capacities by means of a synchronous motor, one winding of which is overexcited by direct current. These two ways are in common use. The second is used mainly in cases where the number of reactive Kva has to be very large.

It is therefore an object of the present invention to regulate the power factor in a single-phase or three-phase electrical distributing network. According to the invention, this system uses appropriate transducers to measure the active and reactive power supplied by the network, determines, by means of suitable circuitry, whether the power factor is above, below, or within acceptable limits and, then, depending on the circumstances, connects or disconnects capacitors in the correct sequence, thus keeping the power factor within the limits specified by the user.

The present invention is therefore concerned with a method of regulating the power factor in an electrical distributing-network line, the method consisting, in its broadest aspect, in

(a) measuring a first component of the power in the line by means of a transducer, the output from which is a continuous voltage proportional to this component of the power supplied by the line;

(b) measuring a second component of the power in the line by means of a transducer, the output from which is a continuous voltage proportional to this component of the power supplied by the line;

(c) dividing the voltage supplied by the transducer of the first component by means of voltage dividers, for the purpose of obtaining two reference voltages L1,L2, the values of which represent the limits specified for the power factor in the line;

(d) comparing the voltage supplied by the transducer of the second component with reference voltages L1,L2 in order to obtain two logic levels indicating one of the three following operations:

(i) connecting one or more capacitors if the power factor is below the limit L1 and is inductive;

(ii) disconnecting one or more capacitors if the power factor is above the limit L2 and is inductive;

(iii) taking no action if the power factor is above the limit L1, and below the limit L2 and is inductive.

The present invention also relates to an apparatus for the execution of the said method.

According to one preferred embodiment of the invention, the active power of the line is measured in watts, after which the reactive power thereof is measured in vars. It is also possible, however, to use a single transducer to measure both watts and vars since a vars transducer is actually a watts transducer, the input potentials of which are 90 out of phase. Another configuration of the invention uses a volt-amperes transducer and a watts transducer. Finally, it is also possible to use a volt-amperes transducer and a vars transducer.

The invention will be better understood from the description given hereinafter, in conjunction with preferred embodiments of the invention illustrated in the drawings attached hereto, wherein:

FIG. 1 is a block diagram of system for regulating the power factor in an electrical distributing-network line;

FIG. 2 is a vectorial representation of the variables describing the power factor;

FIG. 3 is a possible design of a portion of the block diagram in FIG. 1;

FIG. 4 is a second embodiment of the invention;

FIG. 5 is a third embodiment of the invention;

FIG. 6 is a fourth embodiment of the invention.

A proper understanding of the invention requires, first of all, a review of FIG. 2. This is a well-known vectorial representation of the variables affecting the power factor. Assuming that the power factor in an electrical distributing network is to be kept within two specific limits shown in FIG. 2, as L1 and L2, to which have been assigned the arbitrary values of a power factor of between 95 and 99%, then according to FIG. 2:

for L1 :

VARS/WATTS=Tg cos-1 L1 

VARS=(Tg cos-1 L1)(watts),

and similarly for L2 :

VARS=(Tg cos-1 L2)(watts).

Thus, in order to keep the power factor between L1 and L2, the following obtains:

(Tg cos-1 L1)(watts)>VARS>(Tg cos-1 L2)(watts).

To be more explicit, this means that if the network power factor is to be above L1, the vars supplied by the network must be less than a certain proportion of the watts supplied by the network. This may be demonstrated by carrying out the complete calculation for L1 =0.95 and L2 =0.99, which gives the following:

VARS<(Tg cos-1 L1)(watts)

VARS<0.329 watts

VARS>(Tg cos-1 L2)(watts)

VARS>0.142 watts

Generally speaking:

K1 watts>vars>K2 watts

Since the purpose of the system is to regulate the power factor at a relatively high value, constants K1 and K2 are always less than 1. Actually, a constant K1 equal to 1 corresponds to a power factor of 70.7%, and the system may be used commercially for power-factor values above 85%. It is therefore possible to replace constants K1 and K2 respectively by 1/N1 and 1/N2, wherein:

N1 =1/K1 and N2 =1/K2 

which becomes:

Watts/N1 >Vars/>Watts/N2 

wherein N1 and N2 are greater than 1.

Reverting to the previous example, it appears that in order to keep the network power factor between 95 and 99%, the following must obtain:

Watts/3.942>Vars/>Watts/7.018

With reference to FIG. 1, it is now possible to deduce the operation of the system for regulating the power factor in a distributing-network line by initially measuring the active power in watts of the network by means of an appropriate transducer 100, the output J from which is a continuous voltage proportional to the active power supplied by the network. The reactive power in vars of the network is then measured by means of a suitable transducer 110, the output K from which is a continuous voltage proportional to the reactive power supplied by the network. The voltage supplied by the watts transducer is divided by block 120 in order to obtain two reference voltages using points L1 and L2 in FIG. 2. According to the configuration of the invention illustrated in FIG. 3, block 120 may contain two potentiometers 122,124 which are suitably graduated (for example from 70.7 to 100%). Reference voltages L1 and L2 find their way to outputs F and H from block 120. Each of the two voltage dividers in block 120 may consist of any other suitable system. Block 130 contains two voltage comparators 132 and 134 which compare output voltage K from the vars transducer with voltages H and F representing respectively points L1 and L2 in FIG. 2. The outputs from these two comparators constitute signals D and E. Signal D indicates the result of the comparison of the vars measured and indicated by signal K with the limit L2 as represented by signal F. Signal E indicates the result of the comparison of the vars measured and indicated by signal K with the limit L1 as represented by signal H.

The result of this comparison in block 130 supplies, by means of a NAND gate 152 and a NOR gate 154, two logic levels A and B indicating one of the following three operations:

(i) if the power factor is below limit L1 and is inductive, one or more capacitors must be connected;

(ii) if the power factor is above limit L2 and is inductive, one or more capacitors must be disconnected;

(iii) if the power factor is above limit L1 and below limit L2, and is inductive, the system must perform no operation.

Provision should also be made in block 150 to ensure that, if the power factor becomes capacitive, one or more capacitors are disconnected regardless of the value of the power factor in relation to the limits established.

The system described above may make use of one of the two means commonly used to regulate the power factor: i.e. by connecting or disconnecting capacitors in the network line, or by simulating these capacitors by means of a synchronous motor, one winding of which is over-excited in direct current. For greater simplicity, however, this present text will deal only with the regulation of the power factor by capacitive loads, which is the most frequent case.

It should be noted that the combination of blocks 100,110,120 and 130 is sufficient to provide, in most cases, an indication of the operation to be carried out, i.e. the connecting or disconnecting capacitors. The presence of blocks 140 and 150 in FIG. 1 is merely a refinement of the present invention, the purpose of which is to deal with a condition which is possible but highly unlikely in practice. For instance, assuming that a system is keeping the power factor between limits L1 and L2 and that, to this end, voltage has been applied to a certain number of capacitors, then, if at this moment there is a sudden decrease, of sufficient amplitude, in the active power supplied by the network, it is possible, since the system has not had enough time to react, for the power factor to drop below limit L1 and, at this time, to be capacitive. It is obvious that, under these circumstances, signals D and F will indicate a need to connect capacitors (since the actual power factor is below that allowed by limit L1), whereas the reverse operation should be carried out. The purpose of block 140 is therefore to determine whether the power factor has become capacitive, and the purpose of block 150 is to combine signals D and E with signal G, for the purpose of avoiding the possible condition described above.

Block 160 in FIG. 1 comprises electronic flip-flops (not shown), the purpose of which is to connect or disconnect the capacitors in sequence. The purpose of block 170 is to provide block 160 with a real-time clock which determines the period of each operation of block 160. Signals A and B in FIG. 1 control the operations of block 160, while signal L indicates the moment at which all available capacitors have been energized.

Signal L, in conjunction with signal B, may be used to initiate an alarm, since signal B indicates that block 160 should add capacitors and signal L indicates that all capacitors have been energized. This condition indicates, therefore, that there are not enough capacitors or that fuses have been burned out. Signals B and L are combined in block 180 in FIG. 1.

The purpose of block 190 is to provide the system with the power required for its operation. Block 200 in the same figure contains capacitors which are connected to the distributing line, thus closing a reverse-feedback loop. As already indicated hereinbefore, these capacitors may be replaced by a synchronous motor.

FIG. 4 illustrates another configuration of the invention. It is possible to use a single transducer to measure both watts and vars, since a vars transducer is merely a watts transducer with the input potentials shifted through 90. A phase shifter 205 is therefore connected to the input to transducer 200 in order to obtain, at the output therefrom, a voltage K' proportional to the vars supplied by the network. Thus the watts are measured by transducer 200, and voltage J, obtained, for example, by means of a "sample and hold" amplifier, is retained. Similarly, voltage K' obtained from watts transducer 200, which is proportional to the vars, is also retained by means of another "sample and hold" amplifier. This arrangement makes it possible to obtain two signals J and K' with a single transducer, and this may be an economic advantage, bearing in mind the increase in complexity in the system as a whole.

There are also two other ways of correcting the power factor, both of which are based upon the principle of this present invention. In the first of these (FIG. 5), blocks 100 and 110 respectively in FIG. 1 may be replaced by a VA (volt-amperes) transducer 300 and a watts transducer 310. In this case, block 320 determines the VA fraction that the watts must represent in order to keep the power factor within the desired limits.

The second possibility is illustrated in FIG. 6. In this case, blocks 100 and 110 in FIG. 1 are replaced by a VA transducer 400 and a vars transducer 410. Block 420 determines the VA fraction to be represented by the vars at the prescribed limits L1 and L2.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3300712 *Mar 26, 1964Jan 24, 1967Ajax Magnethermic CorpControl device for automatically adding and subtracting capacitors to maintain preselective power output
US3703680 *Feb 8, 1971Nov 21, 1972Asea AbCapacitor bank for ac networks
US3940687 *May 2, 1974Feb 24, 1976Enver Bejukovich AkhundovMethod for controlling active power distribution in power transmission lines and a controller for effecting same
US4055795 *Jul 15, 1976Oct 25, 1977H.O.P. Consulab Inc.Correction system for regulating the power factor of an electrical network
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4353024 *Jun 10, 1980Oct 5, 1982Westinghouse Electric Corp.Control for VAR generator with deadband
US4365190 *Mar 19, 1981Dec 21, 1982Asi Systems, Inc.Automatic var controller
US4771225 *Mar 6, 1987Sep 13, 1988Kabushiki Kaisha ToshibaDevice for limiting switching frequency of a parallel capacitor reactive power compensation network
US4891569 *Aug 20, 1982Jan 2, 1990Versatex IndustriesPower factor controller
US5736838 *Dec 7, 1994Apr 7, 1998Dove; Donald C.High speed power factor controller
US6008548 *Jun 1, 1998Dec 28, 1999Cinergy Corp.Programmable logic controller for resonance control in complex capacitor switching
US6121758 *Jun 23, 1999Sep 19, 2000Daq Electronics, Inc.Adaptive synchronous capacitor switch controller
US6462519Jun 5, 2001Oct 8, 2002Mcdaniel William D.Automatic power factor correction system
US6700358Jun 4, 2002Mar 2, 2004Mcdaniel William D.Automatic power factor correction system
US7002321Feb 27, 2004Feb 21, 2006Mcdaniel William DAutomatic power factor correction using power measurement chip
US20040164718 *Feb 27, 2004Aug 26, 2004Mcdaniel William D.Automatic power factor correction using power measurement chip
CN100468274CJan 13, 2006Mar 11, 2009三菱电机株式会社Power factor adjusting device
EP0168147A1 *May 24, 1985Jan 15, 1986Arthur Trevor Williams (Proprietary) LimitedPower factor controller
EP0239278A2 *Mar 9, 1987Sep 30, 1987Kabushiki Kaisha ToshibaCapacitor apparatus for reactive power compensation
EP0239278A3 *Mar 9, 1987Mar 1, 1989Kabushiki Kaisha ToshibaCapacitor apparatus for reactive power compensation
EP0707216A3 *Oct 13, 1995Sep 25, 1996Gen Electronik Gmbh Bei MagdebMethod and clip-on current probe for determining the compensation capacity of an electrical network
Classifications
U.S. Classification323/211
International ClassificationH02J3/18
Cooperative ClassificationH02J3/1828, Y02E40/30
European ClassificationH02J3/18C1
Legal Events
DateCodeEventDescription
Jan 18, 1994ASAssignment
Owner name: LES INDUSTRIES C-MAC INC., CANADA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CONSULAB, INC.;REEL/FRAME:006838/0318
Effective date: 19920609